Practice Paper -1, 2023–24
Physics (042)
Class – XII (Set – (C)
Time Allowed: 3 Hrs.
Maximum Marks : 70
Name ________________________________
Sign of Invigilator _________
(1)
(2)
(3)
(4)
(5)
(6)
(7)
i.
ii.
iii.
iv.
v.
vi.
vii.
Q1.
Q2.
There are 33 questions in all. All questions are compulsory.
This question paper has five sections: Section A, Section B, Section C, Section D and Section E.
All the sections are compulsory.
Section A contains sixteen questions, twelve MCQ and four Assertions, Reasoning based of 1 mark
each, Section B contains five questions of two marks each, Section C contains seven questions of
three marks each, Section D contains two case study based questions of four marks each and Section
E contains three long answer questions of five marks each.
There is no overall choice. However, an internal choice has been provided in one question in Section
B, one question in Section C, and all three questions in Section E. You have to attempt only one of
the choices in such questions.
Use of calculators is not allowed.
You may use the following values of physical constants where ever necessary
c = 3 x 108 m/s
me = 9.1 x10-31 kg
e = 1.6 x 10-19 C
µ0 = 4π x 10-7 Tm −
h = 6.63 x10-34 Js
−
−
ε0 = 8.854 x10-12
Avogadro’s number = 6.023 X
per gram mole
Section A
In the adjoining figure what is the final value of current in the 20 resistor when the circuit is [1]
completed?
(a) 0.3amp
(b) zero
(c) 0.2amp
(d) 0.1 amp
[1]
A thermocouple of negligible resistance produces an emf of 40 in the linear range of
temperature. A galvanometer of resistance 10 ohm whose sensitivity is 1
, is employed
with the thermocouple. The smallest value of temperature difference that can be detected by
the system will be:
(a) 0.25°C
(b) 0.1°C
(c) 0.5°C
(d) 1°C
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Q3.
Q4.
Q5.
Q6.
Q7.
Q8.
Q9.
When three identical bulbs of 60 - 200 volt rating are connected in series to a 200 volt
supply, the power drawn by them will be:
(a) 60 watt
(b) 10watt
(c) 20watt
(d) 180watt
A proton and an - particle follow the same circular path in a transverse magnetic field.
Their kinetic energies are in the ratio:
(a) 1 : 4
[1]
[1]
(b)
(c) 1 : 1
(d) 1 : 2
A square of side L meters lies in the x - y plane in a region, where the magnetic field is given [1]
by
Tesla, where B is constant. The magnitude of flux passing
through the square is
(a) 4 B L Wb
(b) 3 B L Wb
(c)
(d) 2 B L Wb
A lamp and a screen are set up 100 cm apart and a convex lens is placed between them. The
two positions of the lens forming real images on the screen are 40 cm apart. What is the focal
length of the lens?
(a) 15 cm
(b) 21 cm
(c) 18 cm
(d) 12 cm
A bird flies down vertically towards a water surface. To a fish inside the water, vertically
below the bird, the bird will appear to
(a) move faster than its actual speed
(b) be at its actual distance
(c) move slower than its actual speed
(d) be closer than its actual distance
If I is the intensity of the principal maximum in the single slit diffraction pattern, then what
will be its intensity when the slit width is doubled?
(a) 2I
(b) I / 2
(c) 4I
(d) I
Monochromatic light of wavelength 589 nm is incident from air on a water surface. What is
the speed of refracted light? Refractive index of water is 1.33.
(a)
m/s
(b)
m/s
(c) 3.26
m/s
(d) 2.26
m/s
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Q10.
Q11.
Q12.
Q13.
Q14.
Q15.
Q16.
Q17.
A beam of light of = 600 nm from a distantsource falls on a single slit 1 mm wide and the
resulting diffraction pattern is observed on a screen 2 m away. The distance between the first
dark fringes on either side of the central bright fringe is
(a) 1.2 cm
(b) 2.4 mm
(c) 1.2 mm
(d) 2.4 cm
For forward biasing a p - njunction, the positive terminal of the battery is connected to
(a) n - type crystal
(b) either p - type or n - type crystal
(c) p - type crystal
(d) neither p - type nor n - type crystal
Diode is used as a/an
(a) rectifier
(b) amplifier
(c) modulator
(d) oscillator
[1]
Assertion ((A): In Lyman series, the ratio of minimum and maximum wavelength is .
[1]
Reason (R): Lyman series constitute spectral lines corresponding to transition from higher
energy to ground state of hydrogen atom.
(a) Both A and R are true and R is the correct explanation of A.
(b) Both A and R are true but R is not the correct explanation of A.
(c) A is true but R is false.
(d) A is false but R is true.
Assertion ((A): Electrons in an atom are held by Colombian forces.
Reason (R): The atom is stable because the centripetal force due to Coulomb’s law is
balanced by the centrifugal force.
(a) Both A and R are true and R is the correct explanation of A.
(b) Both A and R are true but R is not the correct explanation of A.
(c) A is true but R is false.
(d) A is false but R is true.
Assertion (R): Increase pressure results in increased activity of a radioactive substance.
Reason (R): Radioactive instability increases with pressure.
(a) Both A and R are true and R is the correct explanation of A
(b) Both A and R are true but R is NOT the correct explanation of A
(c) A is true but R is false
(d) A is false and R is also false
Assertion ((A): The mass number of a nucleus is always less than its atomic number.
Reason (R): Mass number of a nucleus may be equal to its atomic number.
(a) Both A and R are true and R is the correct explanation of A
(b) Both A and R are true but R is NOT the correct explanation of A
(c) A is true but R is false
(d) Assertion is incorrect, reason is correct.
Section B
In a series L - C - Rcircuit, obtain the conditions under which
(i)
the impedance of circuit is minimum and
(ii)
wattless current flows in the circuit.
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Q18.
Q19.
Q20.
Q21.
Q22.
The image obtained with a convex lens is erect and its length is four times the length of the
object. If the focal length of the lens is 20 cm, calculate the object and image distances.
What is the deBroglie wavelength of a nitrogen molecule in air at 300 K? Assume that the
molecule is moving with the root mean square speed of molecules at this temperature.
(Atomic mass of nitrogen = 14.0076 u).
At what speed must the electron revolve around the nucleus of the hydrogen atom so that it
may not be pulled into the nucleus by electrostatic attraction? Given r = 0.5 10
m, me =
9.1 10
kg and e = 1.6 10
C.
OR
Assuming an electron is confined to a 1nm wide region, find the uncertainty in momentum
using the Heisenberg Uncertainty principle( x
p h). You can assume the uncertainty
in position x as 1nm. Assuming p
p, find the energy of the electron in electron volts.
Calculate the value of V and I, if the Si diode and the Ge diode conduct at 0.7 V and 0.3 V
respectively, in the circuit given in figure. If now Ge diode connections are reversed, what
will be the new values of V and I.
Section C
Define electric flux. Write its SI unit.A small metal sphere carrying charge +Q is located at
the centre of a spherical cavity inside a large uncharged metallic spherical shell as shown in
the figure. Use Gauss’ law to find the expressions for the electric field at points P and P .
Show diagrammatically the behaviour of magnetic field lines in the presence of:
(i)
diamagnetic and
(ii)
paramagnetic substances
How does one explain this distinguishing feature?
Q24. The current flowing through an inductor of self - inductance L is continuously increasing.
Plot a graph showing the variation of:
(i)
Magnetic flux versus the current
(ii)
Induced emf versus dI/dt
(iii)
Magnetic potential energy stored versus the current.
Q25. A circuit draws a power of 550 W from a source of 220 V, 50 Hz. The power factor of the
circuit is 0.8. The current in the circuit lags behind the voltage. Show that a capacitor of
Q23.
about
[2]
[2]
[2]
[2]
[3]
[3]
[3]
[3]
F will have to be connected to bring its power factor to unity.
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Q26.
Q27.
Q28.
Q29.
Name the type of EM waves having a wavelength range of 0.1 m to 1 mm. How are these
waves generated? Write their two uses.
In the following diagram, an object ‘O’ is placed 15 cm in front of a convex lens L1 of focal
length 20 cm and the final image is formed at I at a distance of 80 cm from the second lens
L2. Find the focal length of the lens L2.
[3]
Explain the formation of depletion layer and barrier potential in a p - n junction diode.
OR
If a small voltage is applied to a p - njunction diode how will the barrier potential be affected
when it is
(i)
forward biased, and
(ii)
reverse biased? Briefly explain.
Section D
Read the text carefully and answer the questions:
A galvanometer can be converted into voltmeter of given range by connecting a suitable
resistance Rs in series with the galvanometer, whose value is given by
Rs=V/Ig−G
where V is the voltage to be measured, Ig is the current for full scale deflection of
galvanometer and G is the resistance of galvanometer
[3]
[3]
[4]
Series resistort (Rs) increases range of voltmeter and the effective resistance of galvanometer.
It also protects the galvanometer from damage due to large current.
Voltmeter is a high resistance instrument and it is always connected in parallel with the
circuit element across which potential difference is to be measured. An ideal voltmeter has
infinite resistance
In order to increase the range of voltmeter n times the value of resistance to be connected in
series with galvanometer is Rs = (n - l)G.
(i) 10 mA current can pass through a galvanometer of resistance 25Ω What resistance in
series should be connected through it, so that it is converted into a voltmeter of 100 V?
(a) 0.975Ω
(b) 99.75Ω
(c) 975Ω
(d) 9975Ω .
(ii) There are 3 voltmeter A, B, C having the same range but their resistance
are 15,000Ω,10,000Ω and 5,000Ω respectively. The best voltmeter amongst them is the one
whose resistance is
(a) 5000Ω
((b) 10,000Ω
(c) 15,000Ω
(d) all are equally good
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(iii) A milliammeter of range 0 to 25 mA and resistance of 10Ω10Ω is to be converted into a
voltmeter with a range of 0 to 25 V. The resistance that should be connected in series will be
(a) 930Ω
Q30.
(b) 960Ω
(c) 990Ω
(d) 1010Ω
(iv) To convert a moving coil galvanometer (MCG) into a voltmeter
(a) a high resistance R is connected in parallel with MCG
(b) a low resistance R is connected in parallel with MCG
(c) a low resistance R is connected in series with MCG
(d) a high resistance R is connected in series with MCG
Read the text carefully and answer the questions: A point source S of power 6.4 10
W emits mono energetic photons each of energy 6.0 eV. The source is located at a distance
of 0.8 m from the centre of a stationary metallic sphere of work function 3.0 eV and of radius
1.6 10 m as shown in figure. The sphere is isolated and initially neutral and
photoelectrons are instantly taken away from sphere after emission. The efficiency of
photoelectric emission is one for very 10 incident photons.
(i)
[4]
The power received by the sphere through radiations is
(a)
(b)
(c)
(d)
(ii)
(iii)
(iv)
Q31.
(i)
(ii)
(iii)
Number of photons striking the metal sphere per second is
(a) 3.3 10
(b) 3.3 1010
(c) 6.7 10
(d) 6.7 1010
The number of photoelectrons emitted per second is about
(a) 3.3 10
(b) 3.3 1015
(c) 6.7 10
(d) 6.7 1015
The photoelectric emission stops when the sphere acquires a potential about
(a) 3 V
(b) 2 V
(c) 6 V
(d) 4 V
Section E
Write two properties of equipotential surfaces.
Depict equipotential surfaces due to an isolated point charge.
Why do the equipotential surfaces get closer as the distance between the equipotential
surface and the source charge decreases?
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(iv)
Q32.
A test charge ‘q’ is moved without acceleration from A to C along the path from A to
B and then from B to C in electric field E as shown in the figure. (a) Calculate the
potential difference between A and C. (b) At which point (of the two) is the electric
potential more and why?
OR
The capacitance of a parallel plate capacitor is 50 pF and the distance between the plates is 4
mm It is charged to 200 V and then the charging battery is removed. Now a dielectric slab (k
= 4) of thickness 2 mm is placed. Determine:
(i)
final charge on each plate
(ii)
final potential difference between the plates
(iii)
final energy in the capacitor and
(iv)
energy loss.
(i)
State Kirchhoff’s rules.
[5]
(ii)
A battery of 10 V and negligible internal resistance is connected across the diagonally
opposite corners of a cubical network consisting of 12 resistors each of 1 resistance.
Use Kirchhoffs rules to determine
a) the total current in the network.
b) the equivalent resistance of the network
OR
(i) A cell of emf ‘E’ and internal resistance ‘r’ is connected across a variable load
resistor R. Draw the plots of the terminal voltage V versus (i) R and (ii) the current I.
It is found that when R = 4 Ω, the current is 1 A and when R is increased to 9 Ω, the
current reduces to 0.5 A. Find the values of the emf E and internal resistance r.
(ii) A cell of emf E and internal resistance r is connected to two external resistances R1
and R2 and a perfect ammeter. The current in the circuit is measured in four different
situations :
a. without any external resistance in the circuit
b. with resistance R1 only
c. with R1 and R2 in series combination
d. with R1 and R2 in parallel combination
The currents measured in the four cases are 0.42 A, 1.05 A, 1.4 A and 4.2 A, but not
necessarily in that order. Identify the currents corresponding to the four cases mentioned
above.
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Q33.
(a) Consider two coherent sources S1 and S2 producing monochromatic waves to produce
interference pattern. Let the displacement of the wave produced by S1 be given by
Y1 = a cost and
the displacement by S2 be
Y2 = a cos(t + )
Find out the expression for the amplitude of the resultant displacement at a point and show
that
the intensity at that point will be I = 4a2cos2/2.
Hence establish the conditions for constructive and destructive interference.
(b) What is the effect on the interference fringes in Young’s double slit experiment when
(i) the width of the source slit is increased ;
(ii) the monochromatic source is replaced by a source of white light?
OR
(a) Use Huygen’s geometrical construction to show how a plane wave-front at t = 0
propagates and produces a wave-front at a later time.
(b) Verify, using Huygen’s principle, Snell’s law of refraction of a plane wave propagating
from a denser to a rarer medium.
(c) When monochromatic light is incident on a surface separating two media, the reflected
and refracted light both have the same frequency. Explain why.
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